Skip to content

planner: Add new variable named "tidb_opt_selectivity_factor" #20896

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 4 commits into
base: master
Choose a base branch
from
Open

planner: Add new variable named "tidb_opt_selectivity_factor" #20896

Changes from all commits
Commits
Show all changes
4 commits
Select commit Hold shift + click to select a range
cb36063
Add temp.md
qiancai Sep 10, 2025
b273a07
Delete temp.md
qiancai Sep 10, 2025
bf495d9
Update system-variables.md
qiancai Sep 10, 2025
4355b57
Update system-variables.md
qiancai Sep 10, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
10 changes: 10 additions & 0 deletions system-variables.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1593,6 +1593,16 @@ mysql> SELECT job_info FROM mysql.analyze_jobs ORDER BY end_time DESC LIMIT 1;
- 该变量是由 v7.6.0 中引入的 [`tidb_ddl_version`](https://docs-archive.pingcap.com/zh/tidb/v7.6/system-variables#tidb_ddl_version-从-v760-版本开始引入) 更名而来。从 v8.0.0 开始，`tidb_ddl_version` 不再生效。
- 从 TiDB v8.5.0 开始，新创建的集群默认开启 TiDB 加速建表功能，即 `tidb_enable_fast_create_table` 默认值为 `ON`。如果从 v8.4.0 及之前版本的集群升级至 v8.5.0 及之后的版本，`tidb_enable_fast_create_table` 的默认值不发生变化。

### `tidb_opt_selectivity_factor` <span class="version-mark">从 v9.0.0 版本开始引入</span>

- 作用域：SESSION | GLOBAL
- 是否持久化到集群：是
- 是否受 Hint [SET_VAR](/optimizer-hints.md#set_varvar_namevar_value) 控制：是
- 类型：浮点数
- 取值范围：`[0, 1]`
- 默认值：`0.8`
- 该变量用于指定 TiDB 优化器的伪选择率。在某些情况下，当优化器无法根据统计信息推导出谓词选择率时，优化器将使用此伪选择率作为替代值。**不建议**修改此值。
Copy link
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Suggested change
- 该变量用于指定 TiDB 优化器的伪选择率。在某些情况下，当优化器无法根据统计信息推导出谓词选择率时，优化器将使用此伪选择率作为替代值。**不建议**修改此值。
- 该变量用于指定 TiDB 优化器的默认选择率。在某些情况下，当优化器无法根据统计信息推导出谓词选择率时，优化器将使用此默认选择率作为替代值。**不建议**修改此值。


### `tidb_default_string_match_selectivity` <span class="version-mark">从 v6.2.0 版本开始引入</span>

- 作用域：SESSION | GLOBAL
Expand Down